When applying the optimization that disables WHERE clause terms that drive

indexes, make sure not to do so if the term being disabled is a transitive
constraint.  Fix for the problem identified by
[forum:forumpost/eb8613976a|forum post eb8613976a].

FossilOrigin-Name: f1f9b5de3c59489b94963685660b3ddc45eece5535b02fec399b6ece0e38563d

src/wherecode.c

@@ -620,7 +620,22 @@ static int codeEqualityTerm(
     sqlite3DbFree(pParse->db, aiMap);
 #endif
   }
-  disableTerm(pLevel, pTerm);
+
+  /* As an optimization, try to disable the WHERE clause term that is
+  ** driving the index as it will always be true.  The correct answer is
+  ** obtained regardless, but we might get the answer with fewer CPU cycles
+  ** by omitting the term.
+  **
+  ** But do not disable the term unless we are certain that the term is
+  ** not a transitive constraint.  For an example of where that does not
+  ** work, see https://sqlite.org/forum/forumpost/eb8613976a (2021-05-04)
+  */
+  if( (pLevel->pWLoop->wsFlags & WHERE_TRANSCONS)==0
+   || (pTerm->eOperator & WO_EQUIV)==0
+  ){
+    disableTerm(pLevel, pTerm);
+  }
+
   return iReg;
 }